Predicting Cumulative Production of Devonian Shale Gas Wells from Early Well Performance Data, Appalachian Basin of Eastern Kentucky

Transcription

1 Predicting Cumulative Production of Devonian Shale Gas Wells from Early Well Performance Data, Appalachian Basin of Eastern Kentucky Brandon C. Nuttall Kentucky Geological Survey With contributions by Shannon Daugherty Eastern Section AAPG, Lexington, Kentucky 17-Sep Sep-2007 Funding: National Coal Resources Data System, U. S. Geological Survey

2 Geology of Devonian Shale

3 Sunbury Berea Cleveland Three Lick Bed Upper Huron Ohio Middle Huron A shale well is? Top Sunbury to top underlying carbonates Lower Huron Olentangy Rhinestreet

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5 Early Performance Data Well log and completion report Initial Open Flow Rock Pressure Monthly production (805 KAR 1:180, KRS ) Maximum monthly production (Mcf( Mcf) First year cumulative production 5 year cumulative production

6 Data Sets KGS online well completion data Location, completions, IOF, RP Division of Oil and Gas Public production data by month (1997) Gas Technology Institute (GRI) Historic, long-term production data Proprietary,, available to members and contractors

7 Production Data Selection Completed since 1-Jan1 Jan-97 Devonian shale only (not commingled) 60 or more months of non-zero data 310 wells

8 Initial Open Flow Data Exhibits only weak trends No uniform method of acquiring

9 Reported Rock Pressure High and low open flows occur in areas of both high and low rock pressure

10 Rock Pressure vs IOF IOF (Mcf) Rock Pressure (psi)

11 Five-year Cumulative Production Again, weak trends Areas with higher and lower production are often adjacent

12 Initial Open Flow Correlation is statistically significant, but weak 5-year Cumulative (MMcf) y = x R 2 = IOF (Mcf)

13 GTI Cumulative Production Industry rule of thumb is 300 MMcf per well 100% 75% 50% 10 MMcf 692 MMcf 25% 1 year 5 year 10 year 25 year 50 year 0% Proprietary data Billion Cubic Feet

14 Cumulative Gas Production 3 Billion Cubic Feet Class 1 Class 2 Class 3 Class GTI data Years in Production

15 Cumulative Production Over Time Ten-year (MMcf) y = x R 2 = Five-year (MMcf) GTI data

16 Public Production Data Classes 100% Type 4: Red 75% Type 3: Yellow 50% Type 2: Green 25% Type 1: Blue 0% 6 months 1 year 5 years 98 MMcf 59 MMcf 35 MMcf Million cubic feet (MMcf) Data from Kentucky Division of Oil and Gas

17 General Decline Model (Arps( Arps) Hyperbolic: q q = i t 1 ( 1+ bd t)b i Best fit parameters: q i initial production D i nominal decline b decline exponent Special cases: Exponential, b=0: q = t e q i D t i Harmonic, b=1: q t q = 1+ ( D t) i i

18 Solving Exponential: Least squares Hyperbolic: ln Optimization Linear Programming ( q ) = ln( q ) D t + t i Both can easily be done with the built-in functions supplied with spreadsheets, but i

19 Deplete free gas in fractures Best Case: Textbook Data Natural fracturing is key to production Desorbs from fracture faces Desorption and diffusion through shale matrix

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21 Challenges Shut-in Noisy data (no trend) Operational changes Apparent incline

22 Raw Data

23 Normalized q t = q obs q max

24 Rate-Cumulative

25 Semi-log plot

26 Rule of thumb: b 3 to 4

27 Rule of thumb: D i to Many data sets have a decline (i.e., slope) that is not statistically different from 0 (no correlation).

28 For exponential decline, Qi is often less than max production Max production is the initial period For hyperbolic decline, Qi is often greater than max production

29 Qi and maximum production are not correlated

30 Basis of classification 50 th percentile 25 th percentile 75 th percentile Public data from the Kentucky Division of Oil and Gas

31 Public data from the Kentucky Division of Oil and Gas 6moCum = 101.7*MaxAvg r 2 = 0.87

32 Type Declines Average Mcf/d Type 1: 143MMcf Type 2: 78 MMcf Type 3: 46 MMcf Type 4: 23 MMcf Months Five-year cumulative production in million cubic feet

33 Conclusions Shale production data is messy Decline curve analysis and reserves projection is an art Maximum average daily production during the first 6 months is an adequate indicator of future well performance Best wells can be expected to make: 20 MMcf in first year 100 MMcf after 5 years

34 Thanks Oil and gas well search with production data kgsweb.uky.edu/datasearching/oilgas/ogsearch.asp Oil and gas well interactive mapping kgsmap.uky.edu/website/kgsgeology/viewer.asp Project web page